Factors that can affect the imaging appearance of the hemorrhages include hemoglobin level at the time of bleeding, location of the bleeding (brain parenchymal versus extraaxial), oxygen status of hemoglobin, intracellular versus extracellular location of hemoglobin, single versus recurrent bleeding, operative intervention, and obviously time from injury to imaging, to name a few.
Because of this, timing of subdural hematomas should be done based on utilizing imagining findings combined with taking into consideration the onset, progression and severity of clinical findings.
There is data on timing of brain parenchymal hemorrhages using magnetic resonance imaging. This is often grouped according to the following information below, but note timing in only approximate.
- Hyperacute "Hemorrhages in MRI"
- Timing – < 24 hours
- Appearance – Oxyhemoglobin shows up hyperintense on T1 weighted images and hyperintense on T2 weighted images
- Acute
"Hemorrhages in MRI"
- Timing – < 1 week
- Appearance – Deoxyhemoglobin shows up isointense/slightly hypointense to gray matter on T1 weighted images and hypointense to gray matter on T2 weighted images
- Subacute
"Hemorrhages in MRI"
- Timing – 1-3 weeks
- Appearance – Methemoglobin shows up
- Intracellular: Hyperintense on T1 weighted images from peripheral to central; hypointense on T2 weighted images
- Extracellular: Hyperintense on both T1 and T2 weighted images
- Chronic
"Hemorrhages in MRI"
- Timing – > 3 weeks
- Appearance – Generally hypointense on the T1 and T2 weighted images. However there may be multiple compartments with variable signals (especially if rebleeding occurs) with septation; hemosiderin deposition causes low signals
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